free cpumask of vcpupinDef

cpumask doesn't get freed when vcpupinDef being freed, this leaks
memory.

src/conf/domain_conf.c

@@ -858,6 +858,7 @@ virDomainVcpupinDefFree(virDomainVcpupinDefPtr *def,
         return;
 
     for(i = 0; i < nvcpupin; i++) {
+        VIR_FREE(def[i]->cpumask);
         VIR_FREE(def[i]);
     }